1. Field of the Invention
The invention relates to biological treatment of waste through activated sludge and fixed film processes.
2. Description of the Prior Art
Biological treatment of wastewater usually employs either activated sludge or fixed film. Activated sludge is the semi-liquid biomass removed from the liquid flow of wastewater. Before it is fully decomposed by aerobic microbial decomposition, activated sludge is put into aeration tanks to facilitate and further undergo aerobic microbial decomposition. Fixed film reactors use biological aerators that rotate around a central horizontal shaft, which is submerged in wastewater. As the aerators reemerge from the surface of the wastewater, they catch air in specially profiled cells.
A typical activated sludge or fixed film apparatus uses an aeration basin, also referred to as an aeration tank or biotank. The aeration basin provides the oxic environment necessary for nitrification with the activated sludge and fixed film, which use nitrifying bacteria such as nitrosomonas and nitrobacter. Denitrification, however, must occur in an anoxic environment. Therefore, nitrification and denitrification are generally incompatible in the same environment. See U.S. Pat. No. 6,039,873, to Stahler, the entire disclosure of which is herein incorporated by reference. Denitrification also requires a source of carbon as food for the denitrifying bacteria.
A typical activated sludge or fixed film apparatus also uses a separate gravity clarifier, sometimes referred to as a settling tank or gravity separator. The purpose of the clarifier is to remove the suspended solid particles in the wastewater. The solid particles range in size from microscopically fine to rather coarse, and consist primarily of undissolved or unoxidized material, spent bacteria and other microorganisms. The clarifier is usually one of a number of types, including circular, hopper bottom or rectangular.
Once separated from the supernatant liquor, the solid particles settle to the bottom of the clarifier to form sludge. The sludge is then returned to the aeration basin by a return sludge pump. The sludge, which contains viable bacteria and microorganisms, reacts with the wastewater in the aeration basin to further the activated sludge process. The rate of return can vary widely in proportion to the rate of influent flow. Typical rates are 25-100 percent of the influent flow.
Conventional clarifiers, however, require a great deal of space and are difficult to transport. Furthermore, they do not work well where there is a great deal of movement, such as on board a ship. They also make it difficult to precisely control the amount of solids in the effluent.
In addition, prior art systems generally use either a fixed film process or an activated sludge process, thereby foregoing the advantages of the other process. Specifically, the fixed film process is simpler, and provides more stable treatment with lower power costs, while activated sludge is more flexible and meets higher quality effluent standards.
The present invention comprises a waste treatment method and apparatus. The apparatus includes a denitrification chamber that receives waste, typically wastewater, through a first conduit and contains the wastewater along with sludge. The mixture of waste and sludge is referred to as mixed liquor. The mixed liquor is eventually discharged through a second conduit into an aeration basin. The aeration basin includes an aerating device for aerating the mixed liquor. Lighter aerated mixed liquor leaves the aeration basin through a third conduit, preferably located near the top of the aeration basin, and enters a clarifying device. The aeration basin includes a fourth conduit for discharging sludge into the denitrification chamber. The clarifying device separates solid particles from the mixed liquor, resulting in sludge and discharge water. The discharge water is discharged through a fifth conduit as effluent and the sludge is discharged through a sixth conduit into the denitrification chamber or the aeration basin or both.
Preferred embodiments of the apparatus further comprise one or more of the features selected from among the following: a first pump to assist the discharge of sludge through the fourth conduit; an intake mechanism for the first pump that intakes sludge near an expanse of a floor of the aeration basin; a filter apparatus that acts as the clarifying device; a filter apparatus that includes a constant backwash filter; a filter apparatus that includes an air compressor; a filter apparatus with an air compressor capable of generating pressure that helps discharge sludge through the sixth conduit; a conduit arrangement wherein the sludge discharged through the sixth conduit is discharged into the aeration basin, i.e., the sixth conduit terminates in, above or near the aeration basin; a conduit arrangement wherein the sludge discharged through the sixth conduit is discharged into the denitrification chamber, i.e., the sixth conduit terminates in, above or near the the denitrification chamber; a conduit arrangement wherein the fourth conduit and the sixth conduit meet at a junction before they release sludge into the denitrification chamber; a conduit arrangement wherein the sixth conduit is attached to the junction via a venturi; wherein the junction includes a nozzle through which mixed sludge may be released; a second pump that capable of mixing of sludge and waste in the denitrification chamber; a conduit arrangement wherein the second pump is operably connected to the junction of conduits; a conduit arrangement wherein one end of the first conduit is within three feet of the nozzle; the aerating device is a rotary aerator; and/or the apparatus includes both (a) fixed film and fixed film microorganisms and (b) activated sludge and activated sludge microorganisms.
In alternative preferred embodiments, the apparatus comprises a third pump capable of assisting the discharge of sludge through the sixth conduit. The third pump may include an intake mechanism for transferring of sludge from the clarifier to the sixth conduit. These alternative embodiments may have one or more of the additional features listed in the paragraph above. However, at least one of these alternative embodiments envisions the use of a gravity clarifier in place of the filter apparatus mentioned above.
The method of the invention includes one or more of the steps of directing waste through a first conduit and into a denitrification chamber where the waste mixes with sludge to form a mixed liquor; directing mixed liquor that has undergone dentrification in the denitrification chamber through a second conduit and into an aeration basin; aerating the mixed liquor in the aeration basin with an aerating device; directing aerated mixed liquor through a third conduit and into a clarifying device capable of separating solid particles from the mixed liquor; directing sludge that collects in the aeration basin through a fourth conduit and into the denitrification chamber; removing solid particles from the mixed liquor directed into the clarifying device to form recycled sludge and discharge water; directing the discharge water through a fifth conduit as effluent; and directing the recycled sludge through a sixth conduit and into either or both the denitrification chamber or the aeration basin.
In preferred embodiments, the method further comprises treating the waste with both (a) fixed film and fixed film microorganisms and (b) activated sludge and activated sludge microorganisms. It is also preferable to separate the particles from the mixed liquor in the clarifying device through constant flow backwash filtering. In more preferred embodiments, the aerating comprises rotating a rotary aerator in the aeration basin. In still more preferred embodiments, directing basin return sludge through the fourth conduit includes pumping it through the fourth conduit and directing clarifier sludge through the sixth conduit includes pumping it through the sixth conduit. Most preferred embodiments comprise mixing in the denitrification chamber the incoming sludge and the incoming waste.
The method and apparatus of the invention will be better understood by reference to the appended drawings and the following description.